The present invention relates to a plasma processing apparatus, and particularly to a plasma processing apparatus of the induction coupling type in which induction plasma is excited in a process room by applying an RF (radio frequency) power to an RF antenna.
In recent years, with an increase in the degree of integration level of a semiconductor device and an LCD (liquid crystal display), it has become necessary to perform an ultra fine process of the order of sub-micron and furthermore of sub-half-micron. In order to perform such a process in a plasma processing apparatus, it is important to control high density plasma with high accuracy under a low pressure atmosphere, such as between 1 mTorr and 50 mTorr. It is also necessary to form the plasma to have a high uniformity and a large area so as to correspond to a wafer of a large diameter or an LCD substrate of a large size.
In consideration of these technical demands, a lot of approaches have been made to establish a new plasma source. For example, EP-A-0,379,828 discloses a plasma processing apparatus of the RF induction coupling type using an RF antenna. As shown in FIG. 12, the plasma processing apparatus 10 of the RF induction coupling type is designed such that one side, e.g., the ceiling side, of a process room 16, which faces a work table 14 for supporting a target object 12, is made of a dielectric body 18, such as quartz glass. An RF antenna 20 formed of, for example, a spiral coil, is disposed on the outside of the dielectric body 18. An electric field is formed in the process room 16 by applying an RF power to the RF antenna 20 from an RF power supply 22 through a matching circuit 24. Electrons flowing in the electric field are made to collide with neutral particles in a process gas, so that the gas is dissociated and plasma is generated.
An RF power for generating a bias is applied to the work table 14 so that a plasma flow incident on the target surface of the target object 12 is accelerated. An exhaust port 28 communicating with exhaust means (not shown) is arranged at the bottom of the process room 16, so that the inside of the process room 16 can be set to have a predetermined pressure atmosphere. A process gas supply port 30 is arranged at the center of the dielectric body 18 forming the ceiling of the process room 16 to feed a predetermined process gas into the process room 16.
In such a conventional plasma processing apparatus of the RF induction coupling type, a dielectric body, on which an RF antenna is arranged, constitutes the ceiling of a process room, which is kept at a low pressure atmosphere. For this reason, it is necessary for the dielectric body to have a large thickness so that it can withstand a pressure difference between the outside and inside of the process room. As a result, a problem arises such that the coefficient of use of an applied energy from an RF power supply is decreased. This problem becomes prominent in a plasma processing apparatus having a big size for processing a wafer of a large diameter or an LCD substrate of a large surface area.
Further, unlike the apparatus using the gas supply port 30 shown in FIG. 12, there is a conventional plasma processing apparatus of the RF induction coupling type which employs a shower head for supplying a process gas into a process room in combination with an RF antenna, in order to suit an increase in the size of a target object. The shower head generally has such a structure that the process gas fed through a gas supply port flows through a distribution room and is then spouted from a number of small holes into the process room. Therefore, in the plasma processing apparatus of the RF induction coupling type having the shower head, the distribution room of the shower head is interposed between the RF antenna and the plasma generation space of the process room. As a result, part of an RF energy supplied from the antenna is consumed by generating plasma in the distribution room, thereby decreasing the RF energy to be supplied to the process room.